Insertion of transposable elements in AVR-Pib of Magnaporthe oryzae leading to loss of the avirulent function

Abstract

Abstract Background Rice blast is a very serious disease caused by Magnaporthe oryzae. The avirulence (AVR) genes of rice blast are perceived by the corresponding rice-blast resistance (R) genes and prompt specific resistance. A mutation in AVR is a major force for new virulence. Exploring mutations in AVR among M. oryzae isolates from rice-production fields could aid assessment of the efficacy and durability of R genes. We studied the probable molecular-evolutionary patterns of AVR-Pib alleles by assaying their DNA-sequence diversification and examining their avirulence to the corresponding Pib resistance gene under natural conditions in China. Results PCRs detected results from M. oryzae genomic DNA revealed that 162 out of 366 isolates collected from Yunnan Province contained AVR-Pib alleles. Among them, 36.1–73.3% isolates from six different rice-production areas of Yunnan contained AVR-Pib alleles. Furthermore, 36 (28.6%) out of 126 isolates had a transposable element (TE) insertion in AVR-Pib, which resulted in altered virulence. The TE insertion was identified in isolates from rice rather than from Musa nana Lour. Twelve AVR-Pib haplotypes encoding three novel AVR-Pib variants were identified among the remaining 90 isolates. AVR-Pib alleles evolved to virulent forms from avirulent forms by base substitution and TE insertion of Pot2 and Pot3 in the 5′ untranslated region of AVR-Pib. Conclusions Our results revealed that AVR-Pib alleles suffered neutral evolution and divergences that led to overcome specific resistant Pib alleles under field conditions. The TE insertion in AVR-Pib was selected and adapted to rice and other Gramineae species.